1. Field of the Invention
The present invention relates to an information processing apparatus and an information processing method. More particularly, the invention relates to an information processing apparatus and an information processing method for reducing the processing load incurred when a reversibly encoded code stream is transformed into an irreversibly encoded code stream.
2. Description of the Related Art
Today, the use of digital picture data has spread to diverse fields including movie production, medical care services, and still picture photographing. Generally, uncompressed picture data constitutes master pictures that are compressed as needed. Compressed digital picture files are often distributed over networks or written to recording media.
Illustratively, the cinema in digital form is subject to a compression format for movie distribution based on the DCI (Digital Cinema Initiatives) standard. Under the DCI, JPEG 2000 (Joint Photographic Experts Group 2000) Part-1, as part of the ISO (International Organization for Standardization) standards, is utilized as the technique for compression and expansion. The bit rates involved peak at 250 Mbps for a moving picture sequence of XYZ 12 bits (24 Hz) in 4,096×2,160 pixels. Uncompressed master pictures are thus compressed before being distributed or projected onto the screen.
Since the huge data size of uncompressed master pictures is disadvantageous to their storage, the master pictures are often compressed reversibly before being stored. In such cases, the data is not damaged when expanded to its original size.
For example, the resolution of pictures according to the DCI standard is 4,096 by 2,160 pixels, about four times as high as the resolution of HDTV (high definition television). That means the size of uncompressed picture data is enormous. As a result, master pictures are frequently stored after being compressed reversibly into files.
For use, the reversibly compressed files are transformed into JPEG 2000 files which are irreversibly compressed files as per the DCI standard. Because reversible compression and irreversible compression according to the JPEG 2000 utilize different wavelet transformation filters, the file data needs to be temporarily reverted to baseband pictures during the transformation.
Ordinary transcoders handling the above-outlined process decode all code streams of a given reversibly compressed file back into baseband pictures of the same data size as the original baseband master pictures.
Some down decoders decode the code streams into normal resolution images by performing inverse discrete cosine transform using only the coefficients of the low-frequency components in DCT blocks of high-resolution picture bit streams. This type of down decoder is disclosed illustratively in Japanese Patents Nos. 4016166 and 4026238.